Adiyiah began his football career at Feyenoord Ghana.[1] He spent several years in Gomoa Fetteh, where the Academy is based, before transferring to Heart of Lions in 2007. After making his debut in the Ghana Premier League with the club based in Kpandu, at the end of the 2007–08 season he was named Most Exciting Player of the league.[2]

In August 2008, Adiyiah made the move to Europe, being signed by Norwegian top flight club Fredrikstad for a fee of only £100k (approx. €125k as of that date).[1] He made his debut for the club in an away match against Aalesund, on 30 August. He went scoreless in four appearances during the 2008 season, as the team finished second in the league.

The following season he scored twice during the training camp, but has not scored in the four league matches he appeared.[3] He also made his debut in the Europa League, in the second leg of the third qualifying round against Lech Poznań.[4]

In late October 2009, after impressing in the U-20 World Cup, Adiyiah was reported to be close to joining Serie A club Milan. Speculation increased as Fredrikstad announced they had received a bid €500k for the young striker from a big European club.[5] The rumour was eventually confirmed by Milan CEO Adriano Galliani on 1 November,[6] and six days later the Ghanaian signed his new contract, as he had passed routine medical examinations.[7]

The move was ratified on 2 January 2010, the first day of the winter transfer window. However Adiyiah was still not able to play, since he was called up by the Ghana national team to take part in the African Nations Cup.[8] Upon his return, a month later, he also secured an Italian work permit, which he was still lacking, thus becoming definitively eligible to play.[9] Despite this, he was never selected by head coach Leonardo during the remainder of the 2009–10 season. On 25 June 2012, Adiyiah completed a three-year contract with Arsenal Kyiv, ending his three years career with AC Milan.[10]

Adiyiah earned his first call-up with the Black Stars on 3 November 2009, shortly after the U-20 triumph, for a World Cup qualification match against Mali, to be played on 15 November.[22] However he was left as an unused substitute.[23] He did make his senior debut three days later though, in a friendly against Angola.[24] In January 2010, he was part of the Ghanaian team that reached the final at the African Nations Cup. Despite making only two substitute appearances, he showed glimpses of a player for the future.[25]

In June of the same year, Adiyiah was called up to take part in the upcoming World Cup, to be played in South Africa.[26] He made his debut in the competition during the last match of the group stage against Germany, coming off the bench for the final minutes.[27] After being left as an unused substitute in the round of 16, he was sent on in the quarter-finals against Uruguay. In the very last minute of extra time, an Adiyiah's header was saved on the line by Uruguyan striker Luis Suárez, who palmed the ball away with both his hands, resulting in a penalty kick for Ghana and Suarez being sent off. However, Asamoah Gyan smashed the penalty against the bar and the game went to the shootout. Adiyiah took the fourth penalty with his team trailing 2–3, but had his shot saved; Sebastián Abreu seized the chance by subsequently scoring the deciding penalty for Uruguay.[28]